+ I have downloaded the latest version of this theme. This version does not show the icons of the folders (a generic icon without form appears for files and folders in Nautilus). Any ideas? The previous version was good for me. Thanks

I just uploaded a fresh one, it's possible there were some broken symlinks.
It's also possible that you've updated or changed installations since you used the original and the desktop files are now calling for a different icon name. Look inside the .desktop file and see what icon the application is looking for. If it's org,gnome.Nautilus (for example) and one doesn't exist find the nautilus (or whatever icon you like) and link, copy or rename it so an icon exists that the application is looking for.

Please do not link to the unmodified original source, but a git repo with your modifications. Every other iconset here does that, so if you are interested in getting the compensation, please do so too. Use either github or www.opencode.net to add repos and put your modified versions in a fully extracted way there.

Open the .desktop file and see what icon it's looking for. Link, copy or rename the file in this set accordingly.
Gnome apps seem to be installed with some new icon naming convention.

I don't have Android Studio installed, but if you tell me what the change is I'll do an update so other users in the future don't encounter this problem. I ran into the same thing with gnome-boxes today. ;-)

Thanks. I tried your solution, but it did not work. I have searched and found that it is a problem of Android Studio and other IntelliJ software.

If another user has the problem, here is the solution:

1. askubuntu.com/a/652437
2. (alternative) Copy the icon of the app from the folder 'scalable/apps' of the theme, convert it to 'studio.png', and place it in the 'bin' folder of the problematic app, replacing the original icon. Log out or restart.